The trend in integrated circuits toward the use of progressively lower supply voltages has produced dual standards for integrated circuits in contemporary devices. At present, integrated circuits designed for operation with a 3 volt power supply (a "low power supply voltage") are preferred for low power consumption. However, integrated circuits designed for operation with a 5 volt power supply (a "high power supply voltage") continue to be widely used. It is noted here, for purposes of understanding the invention, that a power supply of a nominal voltage, e.g. "5 volts", is understood in the field to mean a supply voltage of approximately the nominal voltage, for example within plus or minus 10% of the nominal voltage.
Devices that employ integrated circuits generally include a power supply that provides either 3 or 5 volts. Some integrated circuit devices provide acceptable performance in some applications with either a low supply or a high supply voltage. However, for other types of devices, the possibility of being used at either of a low or a high power supply voltage imposes mutually exclusive constraints that arise from the majority carrier nature inherent in CMOS processes. For example, for a CMOS comparator operating at a conventional clock frequency, e.g. 44 NHz, a relatively high bias current is required to achieve the slew rate necessary for operation at a high power supply voltage. However, at a low power supply voltage the same biasing current would be excessive and drive the comparator elements beyond the available headroom, wasting power and producing undesirable signal distortion. Therefore, in accordance with conventional practices, IC manufacturers may need to produce multiple versions of an IC that are optimized for operation at different supply voltages.
While 5 volt integrated circuits will eventually be entirely supplanted by 3 volt devices, it is expected that future generation ICs will be designed for even lower supply voltages, for example, 1.8 volts. This will produce another dual standard, requiring further costly duplication of effort to manufacture multiple versions of a single IC.